Abstract

An interruption of the blood supply to the brain, as occurs during ischemic stroke,results in a rapid decline of ATP levels and a subsequent loss of neuronal functionand viability. Under physiological conditions the brain reuses ATP degradationmetabolites, such as hypoxanthine, via the purine salvage pathway, to restore itsATP pool. However, the massive degradation of ATP during ischemia results in theaccumulation and loss of diffusible purine metabolites and thereby leads to areduction in the post-ischemic ATP pool size, leaving the brain more vulnerable tosecondary ischemic insults (recurrent strokes) and less able to deploy reparativemechanisms. The aim of this study was to improve the recovery of post-ischemicATP levels by enhancing the purine salvage pathway, with substances that arealready known to be tolerated in humans.Using acute hippocampal rat brain slices, I found that 1 mM Ribose (Rib) and 50 μMAdenine (Ade), two main metabolites of the purine salvage pathway, significantlyincreased the tissue ATP levels under basal conditions. Rib/Ade pre-treatment resultsin accelerated decline of synaptic transmission after onset of oxygen/glucosedeprivation (OGD), due to increased adenosine release. However, this interventiondoes not delay the onset of anoxic depolarisation, or improve the recovery ofsynaptic transmission after prolonged ischemic periods. Pre-treatment of brain sliceswith 1 mM creatine, which increases phosphocreatine levels and thereby buffers therapid decline of ATP levels upon energy shortage, significantly delays the onset ofAD and helps to improve the recovery of synaptic transmission. By using culturedcerebellar granule cells, for more protracted studies on cell viability after OGD, Ishow that addition of Rib/Ade after ischemia helps to improves cell viability.Therefore my results suggest that both, delaying the decline of ATP upon onset ofOGD (pre-treatment with creatine), or enhancing the post-ischemic recovery of ATP(post-treatment with Rib/Ade) are useful strategies to improve cell survival andfunction after in vitro ischemia.